One type of static seal is a ring-shaped seal that is composed of at least two materials. The core part is a rigid material, and the other part (or parts) is another type of material. The rigid core material is typically a metal, and the second material is typically graphite. The second material is typically attached to both the top and bottom of the core material. Thus, in a typical seal of this type there is a flat, ring-shaped metal core sandwiched between two ring-shaped sheets of graphite.
This type of static seal can be used to seal any faying surface. For example, the seal may function to seal the end of pipeline connections; and bolts, screws, and various flange-type connections may also be sealed.
The seal is placed under an axial load when the two surfaces to be sealed are tightened close together. The second material may be a softer material that conforms to irregularities of the surfaces and enhances the sealing function. It may also be a harder material that enhances the durability of the seal. The metal core functions to give the seal a solid structure and provides resiliency to push against the faying surfaces. The metal core ring can also be used as a seal by itself, particularly in high temperature applications.
Current designs exhibit some problems when subjected to axial compression. As the axial load on the seal increases, the resilient material may have a tendency to be forced out radially from the sealing surface, and the typical core ring has a sinusoidal wave shape that flattens out. Accordingly, seals must intermittently be replaced or repaired because they inevitably wear away or are extruded from the sealing surface. This requires the mechanism on which the seal is acting to be shut down until the seal can be repaired or replaced. Consequently, this entails an expense in lost time while the machine is down, as well as labor and material costs.
When a seal breaks down it may also cause fugitive emissions. Depending on the application, this can cause serious health and environmental problems. With recently heightened EPA restrictions on emissions, the durability and longevity of a seal is extremely important.